FORMATION OF THE ANIMAL TEXTURES. 



xiii 



Fig. V. 



between the cavities is increased. Now, although in certain cases it would 

 seem that this increase is in part due to deposit of intermediate substance 

 independently of the coalescence of 

 thickened cell- walls, yet the process on 

 the whole may be not unaptly com- 

 pared with the formation of the hard 

 tissues of plants from the thickened 

 sides of vegetable cells. Again, during 

 the growth of most cartilages the cells 

 increase in number, new ones being 

 formed within the old, as happens in 

 many vegetable structures. 



The instance now given, and others 

 to the same effect, which will be men- 

 tioned as we proceed, tend to show a 

 certain fundamental resemblance in the 

 process of textural development in the 

 two kingdoms ; but, when we come to 

 inquire into the various modifications 

 which that process exhibits in the 



formation of particular textures, we encounter serious difficulties. The 

 phenomena are sometimes difficult to observe, and, when recognised, are 

 perhaps susceptible of more than one interpretation ; hence have arisen con- 



Fig. V. SECTION OP A BRANCHIAL 

 CARTILAGE OF A TADPOLE, SHOWING 

 THE EARLY CONDITION OF THE CELLS ; 

 MAGNIFIED 450 DIAMETERS (Schwann). 



Fig. VI. CARTILAGE OF 

 THE BRANCHIAL RAY 

 OF A FISH (Cyprinus 

 erythrophthalmus) IN 



DIFFERENT STAGES OF 



ADVANCEMENT f MAGNI- 

 FIED 450 DIAMETERS 



(Schwann). 



Fig. VI. 



flicting statements of fact, and differences of opinion, at present irreconcile- 

 able, which future inquiry alone can rectify, and which in the mean time 

 offer serious obstacles to an attempt at generalisation. In what follows, 

 nothing more is intended than to bring together, under a few heads, the 

 more general facts as yet made known respecting the formation of the 

 animal textures, in so far as this may be done without too much anticipating 

 details, which can only be suitably and intelligibly given in the special 

 history of each texture. 



Structure of Cells. A vegetable cell consists of, 1. a containing wall or 

 envelope, surrounding and enclosing the other parts, and named, from the 

 nature of the substance of which it is composed, the cellulose wall (fig. VIL, 

 a, a) ; 2. the cell-contents fluid, slimy, or of mixed nature (6) ; 3. the 

 nucleus (c), a rounded corpuscle situated somewhere in the interior, which 

 however disappears from many vegetable cells when they have reached 

 maturity. In the nucleus are commonly to be seen one (c) or two (c'), 

 rarely more, minute spots named nucleoli. Further, some phytologists 

 maintain that within the cell- wall, and distinct from it, there is a delicate 

 membrane or film immediately inclosing the cell- contents, the primordial 

 utricle ; but although the semblance of such an interior inveloping film may 

 be brought into view by the application of certain re-agents (as at d), its 



